Every now and then, you'll find diplomatic DOFF missions to delegate with Xindi-Insectoid, Xindi-Aquatic, and various other Xindi races.

Personally, I'm surprised that this game doesn't make much mention of the Denobulans. Doctor Phlox performed well enough onboard the Enterprise to have a ship named after him in this game, yet there's no hide or hair of them anywhere in the game.

There is one. The original captain of your ship is a Denobulan. He dies off-camera about six minutes into the tutorial, though.

As for the Xindi, a lot of the first set of ultra rare doffs were Xindi. All the surviving races are covered, including aquatics. Which raises the question of where on a small ship do you find space for the tank and attendant life support systems to provide living and working space to an inconveniently large whale-person?